The overall objective is to understand at a molecular level the fundamental processes by which bioenergetic membranes function. This includes coupling of the release of oxidation-reduction energy to formation of ATP, and ion and metabolite transport. In the system chosen, that is the photosynthetically competent membrane of Rhodospirillum rubrum, it also means understanding the mechanism and role of the primary photochemical events. In experimental pursuit of these objectives we plan to complete the determination of the primary structure of the light-harvesting (LH) protein of Rhodospirillum rubrum and then establish its three dimensional relationship to the membrane. Associated with this work will be the establishment of the relationship of this complex to the reaction center and any other light harvesting components in the photoreceptor complex. In addition to characterization of the protein-pigment complexes referred to above, we will continue to study the mechanism of photochemical events in R. rubrum by physical probes of the in vivo system and by selected replacement of molecules which serve as the primary electron donor (bacteriochlorophyll) and the first stable electron acceptor (ubiquinone). The in vivo system will also be examined as to the efficiency with which metabolites such as malate or alanine are taken up and how these transport processes are coupled to the energy yielding light capture and secondary electron flow.